Stress is a normal part of life and even a necessary part of development. But not all stress affects the body the same way. Understanding three types of stress helps explain why some adversity strengthens children and other adversity harms them:

Positive stress is brief and manageable. A difficult test, a sports competition, the first day at a new school. The heart rate rises, stress hormones spike briefly, and then the system returns to normal. Positive stress builds coping capacity when the child has supportive adults nearby.

Tolerable stress is more serious but still temporary. A family illness, a natural disaster, the death of a grandparent. The body's stress response activates for longer, but with the buffering of a caring, stable adult relationship, the system eventually returns to baseline. The experience is hard but does not cause lasting biological damage.

Toxic stress is what happens when adversity is severe, chronic, or repeated — and the child does not have adequate protective relationships to buffer the impact. The stress response system stays activated for weeks, months, or years. Without a "shut-off" signal, the body's systems are flooded with stress hormones continuously — and this prolonged activation begins to damage the very systems it was designed to protect.

Toxic stress is the bridge between adverse experiences and physical health problems. It is how trauma gets into the body.

How Toxic Stress Changes the Body

When the brain detects a threat, it activates the hypothalamic-pituitary-adrenal (HPA) axis — the body's central stress command system. This system floods the body with cortisol and adrenaline: the heart rate increases, breathing quickens, muscles tense, and the immune system shifts into emergency mode. This is the fight-or-flight response, and it is designed to be temporary.

Under toxic stress, the HPA axis stays activated. Cortisol stays elevated. The body remains in emergency mode for extended periods. Over time, this chronic activation produces measurable changes across multiple body systems:

The immune system

Chronic cortisol exposure suppresses normal immune function while simultaneously increasing inflammatory markers. The result: trauma-affected teens may get sick more often (weakened immunity) while also developing conditions driven by excessive inflammation — including asthma, autoimmune responses, eczema, and heightened allergic sensitivity.

The endocrine system

Prolonged stress hormone exposure disrupts the hormones that regulate growth, metabolism, and puberty. This can contribute to weight changes, disrupted growth patterns, and in some cases accelerated or delayed puberty. The body is diverting resources from development to survival.

The cardiovascular system

Sustained elevation of cortisol and adrenaline raises blood pressure and heart rate chronically. Over years, this increases the risk of cardiovascular disease. The original ACE study found that adults with four or more ACEs had double the risk of heart disease — even after controlling for traditional risk factors like smoking, diabetes, and cholesterol.

The digestive system

The gut has its own nervous system (the enteric nervous system) that is directly connected to the brain's stress response. Chronic stress disrupts gut function, producing the stomachaches, nausea, appetite changes, and digestive issues that are among the most common physical complaints in trauma-affected children. Research shows that stomachaches are one of the most prevalent somatic symptoms in adolescents with ACE exposure.

The Symptoms Parents Are Seeing Right Now

While the long-term health risks are serious, the symptoms parents notice today are usually the everyday physical complaints that bring them to the pediatrician:

• Chronic headaches — the most commonly reported somatic symptom in adolescents with ACE exposure
• Persistent fatigue and exhaustion — even with adequate sleep, because the body is spending energy on chronic stress activation
• Stomachaches, nausea, and digestive issues — especially before school or stressful situations
• Sleep disruption — difficulty falling asleep, staying asleep, nightmares, or sleeping too much
• Frequent illness — colds, infections, and other signs of suppressed immune function
• Chronic muscle tension, jaw clenching, or back/neck pain — the body holding stress physically
• Unexplained skin conditions — rashes, eczema flares, or hives associated with stress

The critical point for parents: these symptoms are real. They are not imagined, exaggerated, or "all in their head." The body is genuinely in distress because the stress response system is chronically activated. The medical tests come back normal because the cause is not a disease — it is a stress response that has become the body's default mode.

How Trauma Changes Gene Expression: The Epigenetics Story

One of the most striking discoveries in ACE research is that trauma changes not just how the body functions today, but how genes are expressed going forward. Epigenetics refers to chemical modifications that attach to DNA and turn specific genes on or off — without changing the DNA sequence itself. These modifications respond to environmental conditions, including chronic stress.

Yale researchers found that children exposed to chronic toxic stress showed changes in gene expression across the entire genome — affecting not just stress-related genes but genes implicated in immune function, inflammation, and a wide array of diseases. Animal studies have shown that these epigenetic changes can even be passed to the next generation, meaning trauma's biological legacy can extend beyond the person who experienced it.

But here is the critical finding for parents: epigenetic changes are reversible. Studies of adults who received successful trauma-focused therapy showed measurable restoration of epigenetic markers in genes affected by chronic stress. The implication is profound: therapy does not just change how your teen feels. It can begin to reverse the biological changes that trauma caused at the genetic level.

The Long-Term Health Risks of ACEs

The original ACE study and hundreds of studies since have documented a dose-response relationship between ACEs and long-term health outcomes. Among adults with four or more ACEs, the risk increases are striking:

• Heart disease: 2x the risk
• Stroke: 2.4x the risk
• Chronic lung disease: 2.6x the risk
• Depression: 4.5x the risk
• Substance dependence: significantly elevated
• Autoimmune disorders: elevated risk

People with an ACE score of seven or higher who do not smoke, do not drink, are not diabetic, and do not have high cholesterol still have a 360% greater risk of heart disease. This means the health impact of ACEs operates independently of lifestyle choices — the toxic stress itself changes the body's baseline risk.

Understanding this long-term picture is not about alarming parents. It is about making clear why addressing trauma now — during adolescence, when the brain and body are still developing and still plastic — is one of the most important investments in your teen's lifelong health.

Sources: Felitti et al. 1998 — original ACE study health outcomes; ACEs Aware / California — toxic stress framework; PMC 2024 — ACEs and somatic symptoms in adolescence; Yale — genome-wide gene expression changes; Burke Harris — The Deepest Well; epigenetic reversal with TF-CBT.